Project Summary Sleep disturbance is a robust precursor to subsequent self-injurious thoughts and behaviors (SITBs), including suicide completion. Yet, to date, few studies have been conducted to elucidate the mechanisms underlying this association. However, improved understanding of this phenomenon could allow for better ability to predict and intervene on SITBs risk, which fluctuates on a daily basis due to the presence of acute stressors (e.g., one or several nights of poor sleep). Growing evidence indicates a strong relationship between nightly sleep quality (SQ) and next day self-regulatory capacity. Specifically, poor SQ is associated with next day depleted self-regulatory capacity, such that individuals are more emotionally reactive to negative stimuli and are less able to modulate their emotional responses. Negative affect in particular is associated with frequency and intensity of SITBs, especially in individuals who are at higher baseline risk for SITBs. Thus, we propose that self-regulatory capacity may be one mechanism underlying the link between nightly SQ and daily SITBs, and that this relationship is particularly pronounced among high-risk individuals. The goals of this research are to test this hypothesis in a pair of studies using a variety of methods. In the first study, we will use daily experience methods to establish within-subject associations between nightly SQ and daily SITB among high- risk adults (i.e., chronically suicidal adults in an intensive outpatient program), and test negative affect as a mediator for these associations (Aim 1). In the second study, we will directly examine self-regulatory capacity in a controlled context using laboratory methods. Specifically, we will measure the extent that prior SQ (sleep actigraphy, averaged over 3 days) contributes to negative affect in response to a laboratory stressor in both low- and high-risk adults. Further, we will examine self-regulatory capacity (i.e., resting respiratory sinus arrhythmia) as a mediator for this association, and test whether these associations are strongest among those with higher baseline risk for SITBs (Aim 2). Ultimately, findings obtained from this project could lay the groundwork for future research to establish precise clinical indicators and biomarkers for SITBs risk associated with sleep disturbance. Importantly, the goals of the proposed research will be accomplished as part of a tailored research training plan focused on developing expertise in SITBs and psychopathology, sleep, important and cutting edge research methods (e.g., psychophysiology, sleep actigraphy, etc.), and advanced statistical approaches. The proposed plan would also include advanced coursework, close supervision and guidance from experts in the field, scientific writing and presentation experience, and opportunities for advanced clinical training with high-risk individuals and sleep disordered populations.